1. Technical Field
The present invention relates to a method and system for processing printed circuit boards in general and, in particular, to a method and system for applying solder paste to printed circuit boards. Still more particularly, the present invention relates to a method and system for applying solder paste on tape carrier package component sites of a printed circuit board.
2. Description of the Prior Art
Solder paste printing is one of the many methods for applying solder on a printed circuit board. During solder paste printing, a reflowable conductive solder paste is selectively applied to a printed circuit board by a screen printer, prior to placement of electronic components on the printed circuit board.
Typically, a conveyor belt shuttles the printed circuit board first beneath a fixed camera, which records and transmits the position of the printed circuit board to a computer, and then beneath a frame, which holds a stencil corresponding to the printed circuit board. In response to reception of the positional information from the camera, the computer calculates alignment information, which is transmitted to a servo-motor coupled to the frame. The servo-motor subsequently makes adjustments in the x, y, and .phi. coordinates of the frame such that the stencil is properly aligned with the printed circuit board. Finally, the properly aligned stencil is dropped into contact with the printed circuit board, and a squeegee blade wipes across the stencil to push the conductive solder paste through openings in the stencil onto the printed circuit board.
At the completion of the solder paste printing process, the stencil is lifted from the printed circuit board, and the printed circuit board is conveyed from beneath the stencil by the conveyor belt.
Tape Carrier Package (TCP) devices are one of the many types of packaged electronic components that may be added to the printed circuit board after the solder paste printing process. TCP devices are characterized by their size compactness and have high-lead-count with ultra-fine pitch spacing between leads. Accordingly, it is quite difficult to apply the correct amount of solder paste onto the corresponding fine pitch pads of the printed circuit board. In fact, instead of utilizing the solder paste printing process as described above, a more common method for applying solder on a printed circuit board having such fine pitch pads is by solder plating of the entire printed circuit board during the printed circuit board manufacturing. However, this method is expensive, and costs from $4 to $25 per printed circuit board, depending on the board size and complexity.
Consequently, it would be desirable to provide an improved method for applying solder paste on tape carrier package component sites of a printed circuit board that is less expensive.